Why do aircraft wings now go up at the ends?

Aircraft manufacturers claim that winglets, as they are known, cut drag and boost fuel efficiency by up to 5%. Though they have been reported as a new trend, they have been around longer than you may realise.

Nasa first realised their aerodynamic benefits in the 1970s and, as the price of aviation fuel has soared in recent years, winglets have become the latest must-have in the skies. Boeing says requests for winglets on its 737s are up from 10% in 2001 to 50% this year.

Philip Butterworth-Hayes, editor of Jane's Aircraft Component Manufacturers, says: "I reckon you're only looking at 1-2% increase [in fuel efficiency] using a winglet but that is really quite significant. I reckon they will soon be on every airplane."

British Airways has winglets on 57 jumbo jets and 66 shorter haul Airbuses, which were in place when the planes arrived from the manufacturers. Rival operators have invested in kits that equip their older aircraft with the ski-shaped ends. The fins can reach up to 4m above the wing and work by evening out the air flow around the tips.

"It's well-known that modifying the wingtip flow is important," says Kenji Takeda, an engineer with the aerodynamics and flight mechanics research group at the University of Southampton. Soaring birds such as eagles have strong feathers that flip up at the wingtips to reduce drag and give the birds more lift. "Nature, as always, has sussed it out first," Takeda adds.

Winglets could bring other environmental benefits besides saving fuel. The altered air flow around the wingtips also reduces the formation of contrails, wispy streaks of cloud left behind when water vapour condenses around particles of pollution in engine exhaust fumes.

How contrails could influence global climate is still debated, though some scientists say they promote the formation of long-lasting cirrus clouds, which help to trap heat at the Earth's surface. Last year, Nasa scientists said an increase in cirrus cloud cover over the US of 1% a decade since 1975 was down to air traffic.